What Your Belly Fat Can Tell You About Your Future Cancer Risk

Carrying around too much extra weight is a risk factor for several types of cancer, and research has suggested that where you store that extra weight may affect your risk, too. A new study shores up that idea, suggesting that excess belly fat can predict cancer risk just as well as overall body mass index (BMI).

The new paper, published in the British Journal of Cancer, combined data from seven previous studies including more than 43,000 older adults. The participants were followed for about 12 years, during which more than 1,600 were diagnosed with an obesity-related cancer. Being overweight or obese has been linked to 13 types of cancer, including colorectal, breast, and pancreatic.

Overall, the researchers found that every standard-deviation increase in waist circumference—equal to about 4.3 inches—was associated with a 13% increased risk of obesity-related cancers. In comparison, every standard-deviation increase in BMI was associated with an 11% increased risk.

The difference between the two measurements was not statistically significant, suggesting that both are equally good indicators of cancer risk. In fact, all four measures of body size that the researchers tested—BMI, waist circumference, hip circumference, and waist-to-hip ratio—predicted similar risk increases. This is the first study to compare these measurements, in relation to cancer risk, in a standardized way.

In a separate analysis of just colorectal cancer, increases in BMI, waist circumference, and hip circumference were associated with 16%, 21%, and 15% increased risk, respectively. In other words, the authors say, being overweight or obese appears to raise the risk of cancer—no matter how you measure it.

Scientists believe there are several possible ways obesity can fuel cancer growth. Excess weight can trigger inflammation throughout the body, as well as an increase in sex hormones and insulin-related growth hormones, all of which have been linked to cancer.

And it’s not surprising that fat stored around the abdomen seems to be especially dangerous; it’s also been linked to an increased risk of heart disease, diabetes, and premature death.

Lead author Heinz Freisling, scientist at the International Agency for Research on Cancer, says the new study shows that where someone carries fat is just as important for cancer risk as how much fat they have. For some cancers, the findings suggested that waist circumference might be even more important than BMI—but the number of people with those specific cancers was small, he says, and more research is needed to show whether this is really the case.

The study focused on middle-aged and older men and women, mainly because BMI is thought to become less accurate at predicting disease risk as people age. “In addition to knowing one's BMI, paying attention to body fat distribution is particularly important in older adults,” Freisling says.

But the connection between belly fat and cancer likely applies to younger individuals as well, the authors write in their paper. “Overall, our results underscore the importance of avoiding excess body fatness for cancer prevention,” they concluded, “irrespective of age and gender.”